Real quick summary leading up to this - I had used premiere pro for some 3 years prior to ~6 months ago, on various grades of hardware, with zero issues. This problem came up 6 months ago without me making any changes that I know about to my editing presets or export settings, and I have moved to a new computer in the last 3 weeks but the issue persists.
When editing, the preview video is incredibly hitchy. In clean, uncut footage it intermittently plays and drops to 1-2 fps or freezes completely. When I press stop, it takes several seconds for it to actually stop playing, whenever the next frame comes. Using half or quarter resolution makes no difference to observed frame rate. During all this, audio remains constant. When exporting, I went from ~.75 real time to export h.264 to ~1.25-1.5 real time of video.
I have tried using raw and 3 different kinds of proxy format for the editing side, and I have used several different sets of export profiles with no discernable difference made. What is confusing is that I have tried across three different computers and all have the same issue.
2700x + gt1030 4gb with 16 gigs of ram editing from hdd. 9700k + 980ti 6gb with 16 gigs of ram editing from ssd. New PC is 5900x + 3060ti 8gb with 32 gb of ram editing from NVME.
All drivers are up to date, premiere is up to date, and I have trouble shot everything I can think of. There is absolutely no reason that my system currently should be struggling, when prior ~6 months ago my far less capable first PC had zero issues. On the new system, Adobe Premiere is only using a tiny fraction of the available ram, cpu, and gpu resources, despite me making sure that it wasn't restricted in any way.
What gives? Has anyone else experienced these issues? My google-fu has failed me.